/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.sedona.core.knnJudgement;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.PriorityQueue;
import org.apache.spark.api.java.function.FlatMapFunction;
import org.locationtech.jts.geom.Geometry;

// TODO: Auto-generated Javadoc

/** The Class GeometryKnnJudgement. */
public class KnnJudgement<U extends Geometry, T extends Geometry>
    implements FlatMapFunction<Iterator<T>, T>, Serializable {

  /** The k. */
  int k;

  /** The query center. */
  U queryCenter;

  /**
   * Instantiates a new geometry knn judgement.
   *
   * @param queryCenter the query center
   * @param k the k
   */
  public KnnJudgement(U queryCenter, int k) {
    this.queryCenter = queryCenter;
    this.k = k;
  }

  /* (non-Javadoc)
   * @see org.apache.spark.api.java.function.FlatMapFunction#call(java.lang.Object)
   */
  @Override
  public Iterator<T> call(Iterator<T> input) throws Exception {
    PriorityQueue<T> pq =
        new PriorityQueue<T>(k, new GeometryDistanceComparator(queryCenter, false));
    while (input.hasNext()) {
      if (pq.size() < k) {
        pq.offer(input.next());
      } else {
        T curpoint = input.next();
        double distance = curpoint.distance(queryCenter);
        double largestDistanceInPriQueue = pq.peek().distance(queryCenter);
        if (largestDistanceInPriQueue > distance) {
          pq.poll();
          pq.offer(curpoint);
        }
      }
    }
    ArrayList<T> res = new ArrayList<T>();
    if (pq.size() >= k) {
      for (int i = 0; i < k; i++) {
        res.add(pq.poll());
      }
    } else {
      for (int i = 0; i < pq.size(); i++) {
        res.add(pq.poll());
      }
    }
    return res.iterator();
  }
}
